Not enough young people have signed up for Obamacare, according to government figures released Monday.

Young adults aged 18 to 34 only make up 24 percent of the 2 million Americans who have signed up so far. But experts say the number should be closer to 40 percent in order to keep premiums low.

Enrolling young and healthy people is important because they generally pay more into the system than they take out, subsidizing older adults.

Instead, older adults with more health problems are signing up. Adults ages 55 to 64 account for 33 percent of the total signups.

A few states accounted for a huge share of the enrollment. California alone had 23 percent of the signups. California, New York, Florida, Texas, and North Carolina accounted for nearly half the total.

Outreach to young adults will increase in the coming weeks, including a national youth enrollment day on Feb. 15 and targeted outreaches by sororities and fraternities, as well as Voto Latino, which focuses on Hispanic youth.

If more young people don't sign up before the end of the enrollment period on March 31, consumers will likely face higher insurance rates next year.